I had an XPS 13 with the i7 and the 1080P display as a work machine for a while.
Nicely built machines overall, however for the price, it still manages to look a bit cheap. The soft touch patterned plastic around the keyboard is remeniscent of a £200 Packard Bell from the purple shirts, although it is nicer to the touch. The screen bezel also feels a little like matte paint, and is very easy to mark accidentally.
The other major annoyance for me is that you can't open it with one hand, you have to pry it open because the bottom of the laptop isn't substantial enough in weight.
Performance wise it seemed great, and the screen was excellent in terms of quality, battery life was more than I'm used to also. However the lack of USB 2.0 or a disk drive, and the fact that it required Intel RST drivers to be built into a custom Windows install in order to change the OS, makes it an utter pain. It took three people, four weeks, several phone calls to Dell, some BIOS tweaks, a custom OS build, and two memory sticks inserted at the same time, just to install Windows 7 onto it. (compliance)
The keyboard wasn't nice to use either, the travel on the keys is too short, and they are too flat. It was like typing on an Apple keyboard, but worse. Some of the keys are odd sizes too (for example the return key) which means that you often strike the wrong key when typing at any real speed...
In the end I went back to my previous Dell Latitude E7250 with the i5 and 768P display, because it felt more substantial, you can open it with one hand, the screen resolution is more usable, and the keyboard is much nicer.
Not greatly impressed, and would be seriously hacked off with all these little niggles if I had spent so much money on one! They are pieces of art, not practical machines. Even Macbook Pro's manage to be beautiful AND practical.